It is frequently necessary to prepare sheet-metal plates for further processing, for instance to produce pipes, in ship-building or the like, by milling them on the edges. Edge milling machines for this purpose are known, being used for panels or strips which are either moving or at rest.
In simple face milling, the axis of the milling head is located approximately in the plane of the sheet. The characteristic variable for milling is the so-called comma factor k, that is, the ratio between the miller feed per cut S.sub.v to the chip thickness s. In face milling, this comma factor is equal to 1.
In order to increase the comma factor and thus to increase the feed speed, circumferential milling is a further known machining process, where the axis of the milling head is located perpendicular to the plane of the sheet. The cutting angle .beta. is thus smaller than 90.degree.. The comma factor is expressed as K=1/sin.beta.. As a result, the miller feed S.sub.v per cut is substantially greater than the chip thickness s. With an identical chip thickness, identical cutter speed and identical milling depth, it is therefore possible to perform milling with faster feeding. The larger the comma factor, the greater the diameter of the milling head and the smaller the cutting depth.
However, difficulties arise if very high feed speeds are desired. Although an enlargement of the milling head produces a reduction in the cutting angle .beta. and thus an increase in the comma factor, still this is associated with increased demand on the bearings increased space requirements, increased cost and greater difficulty in making a tool change.
If the number of cutters is increased while the diameter remains the same, the distance between cutters is then decreased, as is the chip space which a chip requires to roll out of the way.
The disposition of a plurality of milling heads one after the other results in great expense. The problem also exists of how to guide a curved sheet through a plurality of straight milling stations disposed in series.